Cycle etching is a technique that alternately repeats etching processes and other processes (e.g., deposition processes) for plural cycles to process a workpiece layer into a desired shape. For example, an etching process in the cycle etching is performed by atomic layer etching (ALE) that etches the workpiece layer for one atomic layer or for several atomic layers.
In typical etching, time for etching the workpiece layer is sufficiently secured. Therefore, in the typical etching, a change in light emission intensity with time during the etching can be easily sensed, and the etching end point can be easily detected based on the change in light emission intensity. On the other hand, in the cycle etching, the etching processes for individual cycles are typically performed in short time to cope with the size shrinkage of semiconductor devices. Therefore, it is difficult in the cycle etching to stably sense the change in light emission intensity with time during the cycle etching. Therefore, it is difficult to detect the etching end point of the cycle etching based on the change in light emission intensity.